President Obama reviewed the situation with Tom Vilsack, the agriculture secretary, who called it “the most serious situation” in about 25 years and added that he was praying for rain.

“I get on my knees every day, and I’m saying an extra prayer now,” Mr. Vilsack told reporters at the White House after his discussions with Mr. Obama. “If I had a rain prayer or rain dance I could do, I would do it.”

Mr. Vilsack said 1,297 counties, or roughly a third of those in the nation, had been designated disaster areas. He said 39 more were being added on Wednesday.

More than three-quarters of the nation’s corn and soybean crops are in drought-affected areas, and more than a third of those crops are now rated poor to very poor, Mr. Vilsack said. The price of corn has increased in recent weeks by 38 percent, and the price of beans is up 24 percent. The country may still have the third-largest corn crop in history because earlier good weather encouraged planting, but Mr. Vilsack said the drought would increase food prices into 2013.

The cost of beef, poultry and pork may go down in the short term because those herds are being liquidated, putting more meat on the market, he said. But those prices will probably rise later in the year or early next year.

He declined to speculate on whether the drought was tied to climate change. “All we know is that right now there are a lot of farmers and ranchers who are struggling,” Mr. Vilsack said, adding that the priority should be “what we can do to help them.”